This invention relates in general to bearings which take axial as well as radial loads and force sensing devices suitable for use in adjusting such bearings, and, more particularly, to a process for adjusting such bearings using a compressive force sensor, to a bearing assembly containing a compressive force sensor, and to a compressive force sensor itself.
Some antifriction bearings, which utilize rolling elements of one type or another between concentric races, have the capacity to transfer axial or thrust loads as well as radial loads, and when single row bearings of this character are organized in pairs, one opposing the other, they are well suited for a wide variety of machine applications, not the least of which is in mountings for the road wheels of automotive vehicles. But the bearings, when so organized, require adjustment during installation to achieve the proper setting for operation. If they are set with too much end play, a limited amount of free radial and axial motion exists in the mounting which may manifest itself in wheel wobble. This instability detracts from the performance of the seals that protect such bearings from contaminants. Furthermore, excessive end play causes the load zone to concentrate at a few rolling elements in each of the two rows, and this may diminish the life of the bearing. Preload, on the other hand, produces a very rigid mounting, but also imparts more friction, and while too much preload may cause the bearings to fail early, a light preload extends bearing life and enhances seal performance.
Most trucks use tapered roller bearings at all wheel locations, and these bearings have the capacity to accommodate radial and axial loads. But the size of the typical wheel bearing for a truck and the mass of the hub which it supports makes the bearings of any pair difficult to adjust on the spindles on which they are mounted. One recommended adjusting procedure, which only adjusts for end play, involves making incremental advances of the nut that holds the bearings on their spindle and between such advances making measurements of end play with a dial indicator. More particularly, the spindle nut is turned to a specific torque while the wheel is oscillated to seat the rollers along the races. Next the nut is backed off one turn and then retightened, again while the wheel is oscillated, until a lesser nut torque is achieved. Then it is backed off again a specified amount. With a jam nut turned down against the spindle nut, the end play is measured using a dial indicator. To this end, the mechanic installs the indicator on the wheel with its stylus against the spindle end and moves the wheel axially back and forth while oscillating it, observing the reading on the indicator as he does, the reading so derived being the end play. If excessive end play appears, the mechanic backs the jam nut off, advances the spindle nut slightly, with the amount being largely based on experience, tightens the jam nut, and makes another measurement. If insufficient end play exists, the mechanic follows essentially the same procedure, but backs the spindle nut off instead of turning it down. This trial and error procedure is repeated until the measured end play falls within an acceptable range.
But for many bearings end play is often not the optimum condition for operating such bearings. It concentrates the radial loads at only a few rollers along the raceways and thereby detracts from the life of the bearing. Moreover, the axial and radial free motion identified with it damages the seals and detracts from their ability to form effective fluid barriers. Preload, when not excessive, extends bearing and seal life. But preload is considerably more difficult to measure than end play.
The present invention resides in a process for quickly adjusting bearings without resorting to trial and error techniques. It enables bearings to be set with a known and controlled preload, all quite easily and in minimum time. The process utilizes a force sensor which is embodied in the bearing arrangement itself, but occupies only a very small amount of space. The invention also resides in the bearing arrangement having the force sensor incorporated into it and in the force sensor itself.